The present invention relates to image sensors, and more particularly, towards an image sensor that incorporates a thin film infrared filter.
Image sensors are electronic integrated circuits that can be used to produce still or video images. Solid state image sensors can be either of the charge coupled device (CCD) type or the complimentary metal oxide semiconductor (CMOS) type. In either type of image sensor, a light gathering pixel is formed in a substrate and arranged in a two-dimensional array. Modern image sensors typically contain millions of pixels to provide a high resolution image. An important part of the image sensor are the color filters and micro-lens structures formed atop of the pixels. The color filters, as the name implies, are operative, in conjunction with signal processing, to provide a color image. The micro-lenses serve to focus the incident light onto the pixels, and thus to improve the fill factor of each pixel.
An infrared (IR) filter is typically used in conjunction with image sensors. The IR filter prevents or limits IR radiation from being incident to the image sensor. Many prior silicon-based pixels are reactive to light in the IR region. Thus, if IR radiation is incident on the pixel, the pixel will generate an output signal. This is undesirable in most applications of image sensors, since these image sensors are designed to provide an image based upon light visible to the human eye.
One common prior art method for solving this problem is to provide a discrete IR filter component in front of the image sensor and/or the lens of the image sensor. The IR filter may come in various forms, but may take the form of a coated glass filter. However, this adds to the cost of the entire camera apparatus.